This invention relates to a dock leveler construction and in particular to an improved support system for the deck of a dock leveler.
Dock levelers are commonly used in a loading dock environment to provide a bridge between the loading dock and the bed of a truck. These devices are either pit or box mounted and may store either horizontally or vertically. Actuation of dock levelers may be by the use of hydraulics, or mechanical spring systems.
Given the difference in level between the dock leveler deck and the bed of a truck, some technique must be used to provide for angular motion to compensate for that difference in level. Present systems use either a flexible deck with fixed rear hinges or a rigid deck with floating rear hinges. In the case of a flexible deck, beams are used which have a low torsional rigidity. Examples are the C-channel, I-beam, angle or in some cases special beam structures such as T or lambda beams. In the case of rigid deck construction, the deck plate is generally strengthened by welding to it a box beam to provide a strong composite beam structure. In practice, the box beam is formed of channel which forms a box when the two free legs are welded to the deck plate.
A box beam construction offers numerous advantages. For example, the box beam compared to a C-channel or I-beam has a higher proportion of material at the maximum distance below the plate. This provides a stronger, stiffer composite beam structure for a given weight of steel. Each box beam provides two support ribs for the deck as compared to a single support area in the case of a C-channel. I-beam, angle beam, T-beam or a lambda beam. This provides the deck plate with improved strength and stiffness to withstand highly concentrated loads such as those exerted by fork truck tires. Additionally, a box beam is easier to assemble because it is inherently stable when set in place during assembly. C-channel is marginally stable, but others such as angle, T or lambda beam are unstable and must be held in place during construction.
A significant limitation of box beam construction is that it forms a hollow structure with very high torsional strength and stiffness. Thus, when used in conjunction with dock levelers to provide strength the box beam requires a more expensive floating rear hinge to provide compensation for the out of level condition.